how can disasters be detected using electronic devices

Answers

If you mean in advance, all manner of sensors from seismographs to radar to magnetotelluric devices monitor volcanoes; satellite imagery, radar, and many other sensors are used to monitor the weather; and so on in many ways for many other potential disasters.

If you mean after the fact, then obviously TV, radio, cameras etc can detect the disaster.

Many natural disasters such as hurricanes, landslides, earthquakes, volcanic eruptions, and tsunamis more and more are being scientifically linked to the affects of global warming (the science surrounding tornadoes is more questionable). Not only is this cause to be more aware of what we are doing to our environment, but we must also in the meantime, find ways to predict disasters so that we can save more lives. The answer that rigibson provides is a good one – there is a lot of technology that is used to track all types of natural disasters – too many to be discussed here, but he gives a good overview. However, I think that it is interesting to keep up to date with new technologies that are being developed in order to predict such disasters. For example, IBM has recently come up with a new form of technology to help predict earthquakes and tsunamis: http://www.networkworld.com/community/blog/ibm-says-software-helps-predict-natural-disas. For more information on how natural disasters are linked to global warming please see the links attached.